Thermosensitive recording media containing an electron-donating color-forming substance and an electron-accepting substance which, on heating, undergo a color formation reaction to form a color image are widely used because of their practical convenience as paper for facsimiles and word processors, POS labels, printer paper for various instruments, and cards. With broadening of application of thermosensitive recording media, there has been an increasing demand for suitability to high-speed recording and high durability. In particular, the demands for improvements in sensitivity and preservability of thermosensitive recording media have ever been increasing.
To meet the demands, hundreds of substances have been studied to date as color developability-improving agents. Among them, benzyl oxalate derivatives, benzylbiphenyl (see JP-A-60 -82382 corresponding to EP-B-164417 and U.S. Pat. No. 4,672,401), benzyloxynaphthalene (see JP-A-58-87094 corresponding to U.S. Pat. No. 4,471,074 and GB Patent 2112951B), ethylene glycol diphenyl ether derivatives (see JP-A-60-56588 corresponding to EP-B-141170 and U.S. Pat. No. 4,531,140), m-terphenyl (see JP-A-57-89994), and so forth have been widely put to practical use. However, having their several merits and demerits, none of them satisfies both the requirements for high sensitivity and high preservability at a time. Hence, it has been demanded to develop a color developability-improving agent excellent in sensitivity and preservability.